This disclosure generally relates to automated systems and methods for stand-off inspection of structures, such as aircraft components. In particular, this disclosure relates to automated methods and systems for locating visible differences on a structural component from a distance and accurately measuring the locations of potential damage relative to a coordinate system of the inspected structure.
Finding and accurately measuring the locations of potential damage on a structure, such as a large commercial airplane, can be a laborious task. An efficient and automated process for addressing this problem would be valuable to many organizations involved in building and maintaining large vehicles and structures.
From two-dimensional images alone, it is difficult to get accurate measurements of aircraft locations defined in aircraft coordinates. Often, an item of known dimensions (like a tape measure) is inserted in the picture to give the analyst a size reference. But even with a reference scale, it can be difficult to measure a precise position in the desired coordinate system. Determining the correct location is especially difficult in areas where few uniquely identifiable landmark features exist. In addition, human analysis of a large number of potential damage areas would likely be error prone. Therefore, it would be desirable to have as much of the damage detection and localization process as automated as possible. Moreover, the entire process should be capable of being performed from a distance, without the need for any of the inspection or positioning equipment to contact the structure being inspected.
One specific problem in automated inspection is to provide a system and a method for automated inspection of dielectric tops on an aircraft wing. A dielectric top is a barrier dielectric patch which covers the head of a fastener to prevent lightning strikes from penetrating the structure and entering the fuel tank area. It is known that dielectric tops are susceptible to cracking after a certain number of years in service. An operator of aircraft so equipped tries to identify cracked dielectric tops in an accurate and fast manner, and then measure the depth of those cracks in an accurate and fast manner. Cracks above a certain length may require repair or replacement of the dielectric tops.
The existing solution for dielectric top inspection is a completely manual visual inspection and repair. Cracks greater than 0.1″ in length are not allowed. Inspecting for these cracks will impact the service readiness of the airplane. Moreover, a typical airplane has about 18,000 dielectric tops.
It would be desirable to combine a stand-off local positioning system with a stand-off nondestructive evaluation (NDE) method to replace inspector's manual labor, increase the inspection rate, and find much smaller cracks than what can be seen visually, without physically touching the aircraft. To speed up an inspection, multiple stand-off NDEs could be run concurrently if multiple local positioning systems were available.
More generally, there is a need for stand-off NDE combined with a local positioning system that provides locating capability in a local (e.g., aircraft) coordinate system. An in-service NDE involving the capability to scan an aircraft structure without having to touch it, while obtaining all the location information without touching it, and to do so concurrently, would be very advantageous.